1. Field
One embodiment of the present invention relates to a disk drive. More particularly, the invention relates to a technique of controlling the positioning of the head, by using spiral servo patterns.
2. Description of the Related Art
In most disk drives, a representative example of which is a hard disk drive, a servo pattern (servo data) that is used to control the positioning of the head is recorded on a disk, which is a data-recording medium. The servo pattern is used to move the head to a target position (i.e., target track) over the disk.
The servo pattern recorded in the disk consists of a plurality of servo sectors. In most cases, the servo sectors are arranged at regular intervals in the circumferential direction of the disk. The servo sectors extend in the radial direction of the disk, constituting concentric servo tracks. The servo pattern, which consists of radial servo sectors (or concentric servo tracks), has been recorded in the disk by performing a servo write operation during the manufacture of the disk drive.
In recent years, it has been proposed that a plurality of spiral servo patterns be recorded in a disk as base pattern (seed pattern), and that a plurality of radial servo patterns be also in the disk based on the spiral servo patterns (i.e., multi-spiral servo pattern). (See, for example, U.S. Pat. No. 7,068,459 B1.)
In this case, the radial servo patterns are servo patterns (hereinafter referred to as product servo patterns, whenever necessary) that are used when the disk drive is used after shipped as a product from the manufacturer. Hence, the multi-spiral servo pattern is finally erased from the disk by over-writing data.
In most cases, a disk having a multi-spiral servo pattern recorded in it is incorporated into the disk drive, and then the disk drive performs a self-servo write operation, writing radial servo patterns (i.e., product servo patterns) in the disk.
When the read head included in the head reads the multi-spiral servo pattern, it generates a detection signal. Based on the detection signal, the disk drive calculates a positional error in order to control the head positioning in preparation for the recording of radial servo patterns. In most disk drives, the head has a read head for reading the servo patterns and a write head for writing the servo patterns, which are spaced from each other. The read head is less wide than the write head. Therefore, the detecting signal the read head outputs upon reading the multi-spiral servo pattern has a hexagonal shape.
The method of calculating the positional error, which is performed to control the head positioning, is an operation (algorithm) that is based on the radial servo patterns. It is desired that the hexagon-shaped detection signal be used in this method of calculating the positional error.
While the positional error is being calculated, the position of the head over the disk may greatly change due to disturbances. In this case, the positional error calculated may not be sufficiently accurate if the detection signal is used, which the read head has output upon reading the multi-spiral servo pattern.